Recently, a cancer treatment using irradiation of high-energy carbon ions has been developed. Ion accelerating apparatuses have actually been installed in general hospitals, and treatment with such apparatuses has already been started. To further improve the performance of the apparatus of this type, an ion source which generates high-density hexahydric carbon ions is indispensable. Conventional ion sources using microwave discharge plasma are insufficient in this respect, and development of a new ion source has been strongly desired.
A laser ion source has been developed as an ion source having the ability to generate a high-density ion beam. This laser ion source applies converging laser light to a target, ionizes the target by laser light energy, and electrostatically extracts ions generated from the target to generate an ion beam.
However, the laser ion source of this type has the following problem. Laser ion sources also involve the generation of particulates during laser irradiation, which accumulate in the case housing of the source. Some of the particulates move to a vacuum evacuation device, and, for example, when a turbo-molecular pump is used, enter a bearing and prevent normal rotation or attach to a blade and become a cause of reduction in exhaust efficiency. Some of the particulates are guided outside the ion source, and adversely affect a device connected to the ion source.
To give energy sufficient for practical use to the ion beam extracted from the ion source and to control convergence, a device including a group of acceleration electrodes or an electrostatic lens is connected downstream of the ion source. In the case of use of an accelerator, a linear accelerator, such as an (raid frequency quadrupole (RFQ), is connected. In the case of use of an ion implementation device, a deflection device or an electrostatic lens is connected. This leads to complexity regardless of the configuration, and the interior of the apparatus is required to be maintained in a clean state. Therefore, release of particulates from the laser ion source is a big problem.